I've got HFC's but the rest of the system is standard, albeit with a little blow in the usual place before the back box and mine failed first, but once they got really hot they were fine. The problem is yours won't get hot with your cooling fans not working. If the bore on the tail pipe is too extreme that will effect the result, but nothing popping a couple of rags in the end won't fix, but not every test station is prepared to do that.